Notebook
• Bound (no spiral notebooks)
• Write in ink
• Always write directly into your notebook
(no transferring data after lab)
• If you have a messy notebook I know you
are using it!
• Pages numbers and dates
• Partner’s name
• Drawing of the apparatus (what did the
calorimetry set-up look like?)
Sample Experiment
Stephan ie End sley
Lab partner: Katy Olsen
10/4/05
HessΥs Law
Purpose: To use a set of calorim etry expe rim ents to determi ne the he at of combustion o f Mg.
Reactions/equations:
Mg(s) + 2HCl(aq)
MgCl2(aq) +H2(g)
MgO(s) + 2HC l( aq)
MgCl2(aq) + H2O(l)
Mg(s) + 1/2O2(g)
q = C x m ass x T
MgO (s)
q = H (constant pressure)
Hrxn = Hc = Hf(produc ts) - Hf(reactants)
Proce dure:
Part 1
1.
2.
3.
4.
5.
Add 25mL of 1M HCl into a styro foam cup.
Add magne tic stir bar into the cup and b egin s tir ring.
Let the temperature become stable and record temperature (Ti).
Weigh a ribbon of magnes ium and coil it loosely.
Add Mg r ibbon into the cup and record the temperature until the it no longer ris es.
Part 2
1. Repeat the above steps only wit h 0 .250g of MgO.
Data:
Part 1
Intial
Temp
.
(C)
Final
temp
.
(C)
T
(C)
Trial 1
22.1
46.0
23.9
Mass of
calorimete
r
(g)
Mass of
HCl +
calorimete
r
Mass
of HCl
in cup
Volume
of HCl
(L)
Molarit
y of
HCl
(mol/L)
0.0254
1.146
Mass
of Mg
(g)
Mass
of
MgO
(g)
Trial 2
Part 2
Trial 1
Trial 2
Observations:
Write down any thing that happens during the experiment.
After adding Mg to the cup, there was a gas given off that smelled bad.
After heating the reaction, for 5 minutes the mixture turned brown.
Calculations:
Moles of HCl = 0.025L x 1mole/L = 0.025moles
H(step 1) = C x (mass of Mg + mass of HCl) x T
Discussion/ postlab questions:
Answer the postlab questions.
Talk about the answers to the calculations that you got. In the Hess’s law experiment: Did the
enthalpy of combustion that you calculated match the theoretical enthalpy? Talk about possible
errors in the experiment that could have contributed to the fact that your answers are different.
Final Lab Reports
2 things:
1) Write out a lab report that includes the
above
2) Make a copy of the experiment from your
lab notebook and turn it in as the final
report
•
If you have carbon copies, you can turn
those in as long as I can read them
•
It is OK if it is messy as long as all of
these things are in the report (purpose,
procedure, equations, data, calculations,
post lab questions, and discussion)